Catalytic oxidation of methane over CeO2-ZrO2 mixed oxide solid solution catalysts prepared via urea hydrolysis Original Research Article

In this study, CeO2-ZrO2 mixed oxide catalysts were prepared via urea hydrolysis and tested for methane oxidation. Highly uniform solid solution particles of ceria-zirconia were obtained under the conditions of this study. The incorporation of Zr into the CeO2 lattice was found to promote the redox properties. The methane oxidation activity of the mixed oxides was found to be dependent on the Ce:Zr ratio, which relates to the degree of reducibility. It was postulated that the cubic phase, fluorite structure, which is mainly found in Ce1 − xZrxO2 (where x<0.5) can be reduced more easily than the tetragonal phase found in Ce1 − xZrxO2 (where x>0.5). The catalytic activity decreased with an increasing Zr content. The mixed oxide catalyst, Ce0.75Zr0.25O2 solid solution, was reported to exhibit the highest activity for methane oxidation. Kinetic studies of methane oxidation over such a mixed oxide catalyst (Ce0.75Zr0.25O2) showed that the methane oxidation rates strongly depend on methane concentration, but only slightly on the oxygen concentrations. The Langmuir–Hinshelwood mechanism (oxygen dissociative chemisorption on the active sites and non-dissociative chemisorption of methane) can satisfactorily fit the experimental results obtained from the kinetic studies for this catalyst. The activation energy of methane oxidation is calculated based on this surface reaction mechanism as being 100.8 kJ/mol.